Absence of the intron-D-exon of c-Ha-ras oncogene in the hermaphroditic fish Rivulus marmoratus (Teleostei: Rivulidae).

We have cloned ras genes from the hermaphroditic fish Rivulus marmoratus genomic library by screening about 3.0 x 10(5) genomic clones. When one out of 19 ras genomic clones was sequenced, it showed 95.8% amino acid homology to the human c-Ha-ras gene and was named the Rivulus c-Ha-ras gene. The Rivulus c-Ha-ras gene spanned about 3.7 kb and consisted of four exons encoding 189 amino acids. The exon-intron boundaries also coincided with the rule of GT/AG of consensus splice acceptor and donor sequences. The Rivulus c-Ha-ras gene does not, however, have the intron-D-exon (IDX) that has been reported to exist between the third and the fourth exon of the mammalian c-Ha-ras genes, and which is involved in negative control of p21 c-Ha-ras expression and transforming activity of this gene. This is the first report on the structure of the fish c-Ha-ras gene.